1. Field of Invention
The present invention relates generally to the field of wireless communication and data networks. More particularly, in one exemplary aspect, the present invention is directed to compensating for or mitigating the effects of electro-magnetic signal interference between devices or components implementing wireless air interfaces.
2. Description of Related Technology
As wireless spectrum continues to become increasingly more crowded, neighboring wireless systems are increasingly faced with the challenge of sharing that scarce spectrum with incompatible neighboring systems. This incompatibility occurs because the wireless protocol standards that govern the interaction of devices within a wireless system are different. These wireless protocol standards generally have at least two main components or layers, a physical or PHY layer, and a medium access control or MAC layer. Incompatibilities between wireless systems can exist in either or both of these layers.
For example, in the United States, wireless systems based on the Bluetooth protocol standard occupy the 2.4 GHz to 2.4835 GHz band, which is the same frequency band used by microwave ovens, some cordless phones, and garage door openers. The Bluetooth devices share this spectrum by utilizing a physical layer technology called frequency hopping spread spectrum (FHSS), to avoid interference from these devices. However, IEEE 802.11b-based and IEEE 802.11g-based wireless systems also occupy the 2.4 GHz to 2.4835 GHz band. These systems utilize physical layer technologies such as Complementary Code Keying (CCK) and/or Direct Sequence Spread Spectrum (DSSS), which can interfere with the FHSS used by Bluetooth. Coexistence between Bluetooth systems and these IEEE 802.11 systems requires additional mechanisms and recommended practices that are being developed by the IEEE 802.15 working group.
In addition to the challenge of sharing spectrum between Bluetooth and IEEE 802.11 systems, the FCC recently awarded the 3.65 GHz spectrum band to both IEEE 802.11y, and IEEE 802.16h systems, with a requirement that the systems coexist in a manner that minimizes interference to their neighboring wireless systems. Similarly the FCC has opened the 700 MHz TV Whitespace spectrum band for coexistence between wireless networks and regulatory incumbents (sometimes called primary and secondary users). Ideally, new wireless networks should minimize their interference with incumbent users. For example, new wireless devices that seek to reuse TV whitespace spectrum, should peacefully coexist with legacy devices (such as wireless microphones).
The FCC identifies two mechanisms for minimizing interference in coexisting wireless systems. The first solution proposes that operators “make any effort” to minimize interference by registering their base station locations, and coordinating their operations to minimize interference. Alternatively, or in combination, a second solution is additionally suggested which allows the use of unrestricted contention protocols that “are broadly compatible and function to prevent interference even with other dissimilar contention technologies on the market”. Over time, the combination of heavily reused wireless spectrums, and the widespread, disorganized usage of dissimilar systems suggests that the proximity of differing wireless technologies will continue to shrink, causing an increase in undesirable interference to neighboring systems.
The effective implementation of convergence products has led to a revolution in the way consumers view computerized devices. These next generation computerized devices focus on offering consumers a substantially unified solution for a variety of services to which consumers have become accustomed. Examples of such converged solutions include the exemplary “MacBook Air” laptop computer, and iPhone™ each manufactured by the Assignee hereof, which support a variety of wireless protocols and other functions. For instance, the iPhone has the capability of, among other things, sending and receiving emails over a wireless LAN (WLAN) network, making and receiving calls using a GSM or 3G cellular network, and operating wireless peripheral equipment (such as wireless headsets) using the Bluetooth (BT) protocol.
When it comes to coexistence between wireless systems sharing the same frequency band, the impact of any system on its neighbors will depend on both the protocol design and implementation of the system in question, and the protocol design and implementation of the neighboring systems. Furthermore, measuring the performance of the coexistence community using a single metric (e.g. such as channel occupancy) is often ineffective because different systems use different PHY and MAC technologies. For example one system may be more sensitive to the decrease in channel occupancy required to support coexistence than a coexisting but different system. This can apply to other metrics as well, such as latency, throughput, bandwidth allocation, etc. The wireless protocol standards of the neighboring systems may adversely affect each other in various ways and in varying amounts that can be interrelated.
Some systems are designed to accommodate environments with interfering systems. For example, in an Orthogonal Frequency Division Multiple Access (OFDMA) system, certain frequency tones may be disabled when the system experiences high levels of interference on those frequency tones. This selective tone usage may enable a transmitter and receiver to determine which frequency tones to disable, thus allowing the OFDMA system to share the same frequency band with a neighboring system. An analogous modification could be performed in the time domain. In both of these cases, the total current throughput for the OFDMA system may be held constant by moving the system traffic to non-interfering physical resources, whether frequency tone-based, or time-based. Thus, OFDMA carefully manages how much of a physical resource is being occupied by a system, as well as the specific resources it occupies, and when those resources are occupied, in relation to all neighboring systems (including other systems that do not use OFDMA as a spectral access technique).
Not all systems have the flexibility of OFDMA technologies. Every wireless system is designed with different protocols at both the physical (PHY) and medium access control (MAC) layers to address the needs of a particular set of application requirements. For example, OFDMA-based systems such as IEEE 802.16 are relatively more concerned with data throughput in their design and architecture than systems based on the IEEE 802.15.4 Low Rate Wireless Personal Area Network standard (referenced subsequently herein), which generally are more concerned with data reliability (which lowers power consumption and reduces latency).
In addition, the traditional measures of link quality—received signal strength indication (RSSI), header error check (HEC) failure rate, cyclic redundancy check (CRC) failure rate, bit error rate (BER), and packet error rate (PER), etc.—do not consider the impacts of neighboring systems. Hence, when interference is present from neighboring systems, traditional link quality measurements may produce misleading results that cause the device to incorrectly respond. For example, the devices within a coexistence community of interfering networks may decide to boost their power as a result of increased BER. If the devices were operating in isolation, boosting transmit power would reduce the BER. However, when performed in a coexistence community, the increased transmit power of each member further exacerbates the interference of the community.
In another example, the devices within a coexistence community may adjust their modulation and coding scheme (MCS) to compensate for high BER. If the devices were operating in isolation, reducing the data rate and increasing channel occupancy would improve the BER. However, in a coexistence community, each device which increases its channel occupancy worsens the overall channel capacity. Traditional approaches do not work well when used in coexistence communities. Thus new approaches are needed for coexistence communities which re-interpret the meaning of link quality, both in isolation, and in relation to other devices.
Traditional approaches fail to produce a globally optimal solution that balances the differing objectives of coexisting wireless systems across a wide variety of performance metrics, where each wireless system may differ according to wireless protocol standard and mix of application usage, and therefore, differ by sensitivity to each performance metric. Accordingly, improved methods and apparatus are needed for enhancing the local performance of neighboring wireless systems against their local objectives, within the context of balancing the competition for access to resources (e.g. frequency bands, time slots, spreading codes, etc.) inherent in coexistence between wireless systems.
Ideally, such improved methods and apparatus would promote the existence of a “good neighborhood” by understanding the behavior of wireless modules within a given converged device, as well as the behavior of other devices in the neighborhood, and adjusting operating behaviors (whether dynamically or statically) in order to benefit the neighborhood as a whole. Such a holistic approach would not only benefit the converged device implementing the policies, but also the broader coexistence community in general.
Such improved methods and apparatus would also ultimately provide the users of the coexistence community with the best user experience possible, while offering converged services in a space and power-efficient manner.